Last year, astronomers discovered a remarkable planet orbiting another star: it has a mass and radius that puts it in the "super-Earth" category — meaning it’s more like the Earth than a giant Jupiter-like planet. Today, it has been announced that astronomers have been able to analyze the atmosphere of the planet (the very first time this has ever been accomplished for a super-Earth), and what they found is astonishing: the air of the planet is either shrouded in thick haze, or it’s loaded with water vapor… in other words, steam!

[Click to embiggen the artist illustrations of the planet and star.]

This is very cool news. Um, hot. Whatever.

Here’s the deal: GJ 1214 is a dinky red dwarf star 42 light years away. It’s only about 1/5th the size of the Sun, and shines with only 1/300th of the Sun’s brightness. A project called MEarth studies such nearby red dwarfs, looking for dips in their starlight that indicate the presence of a planet: when the planet passes in front of the star (called a transit), it blocks the light a little bit.The cool thing about transits is that if we know the radius of the star and how much the light dips, we can immediately get the size of the planet! The bigger the planet, the more light is blocked. If the planet blocks, say, 1% of the light, then it has a radius 1/10th that of the star (the area of the disk of the planet is related to the radius of the planet squared, so if the planet’s radius is 0.1 times the star’s, then the area of the planet’s disk compared to the star’s disk is 0.1 * 0.1 = 0.01 = 1%).

In 2009, astronomers found just such a dip in GJ 1214’s light, meaning there was a planet there (called GJ 1214b). The radius of the planet turns out to be about 2.6 times that of the Earth. That’s much bigger than we are, but still much smaller than Jupiter (which is 11 times the Earth’s diameter). But don’t go thinking it’s Earthlike: it orbits the red dwarf at a distance of only 2 million kilometers, screaming around the star once every 38 hours! Even though the star is much cooler than our Sun, from that distance the planet gets cooked to a temperature of about 200° Celsius (~400° F). Ouch.

The thing is, the way the light dipped indicated the planet was bigger than models indicated it should be. One thing that can do that is an atmosphere, in this case one about 200 km (120 miles) thick — much thicker than ours.

Astronomers observed the planet when it passed in front of the star, analyzing the light very carefully. As starlight passes through the planet’s atmosphere, certain colors of it get absorbed, and these are like fingerprints that can be used to figure out the atmospheric composition. Most models predicted a heavy hydrogen content, but the observations indicate none is there! That means either there are thick layers of haze in the upper atmosphere of the planet, obscuring any hydrogen below them — much like Venus or Saturn’s moon Titan, blocking the view lower down — or there is a vast amount of water in the planet’s air. And at a temperature of 200° C, that water would be in the form of vapor. In other words, steam.

Steam! Amazing.

It’s unclear which scenario is more likely, but either way this is an amazing accomplishment. I suspect (opinion time here!) that water vapor is the culprit; according to the astronomers’ data, there aren’t any known haze particles at the pressure and temperature indicated that could form clouds thick enough to explain the observations. That doesn’t mean there is no haze; just that current models of how these processes work come up empty for this situation. And more observations may yet be able to distinguish between haze and water vapor in the planet’s air.

But there’s something else I was to add, something I haven’t seen in the papers or the press releases. Observations of how hard the planet is tugging on its star have yielded the mass of the planet: it’s 6.5 times as beefy as we are. So we have the mass and the radius of the planet, and that means we can calculate many other features, like its density — which turns out to be very low, only about 1/3 the density of the Earth! That means this planet must be very deficient in heavy metals compared to the Earth, or else it would be much denser.

Interestingly to me, having the mass and radius also means we can find the surface gravity of the planet: in other words, how strongly gravity would pull you down if you stood on its surface. Given the large mass, you might expect the gravity to be much stronger than Earth’s, but in fact when I did the math I was surprised to find that the surface gravity is almost exactly the same as we feel here on Earth!

I know this is a distant world, much larger, more massive, and hotter than Earth, shrouded in a thick atmosphere far different than ours, orbiting a Sun about as different from ours as can be… but weirdly, knowing I’d weigh about the same standing there as I do here somehow makes the planet seem a lot less, well, alien.

It’s easy to forget that these aren’t just distant points of light, or simple artist drawings. These are worlds. And every one of them is different, strange, wonderful, and awe-inspiring.

And this new result serves as a brilliant reminder: we live in an age where we can taste the air of alien planets from trillions of kilometers away!

Hi Phil – the article and your writeup say that they were unable to
determine whether the atmosphere contained water vapour or some other
haze, yet they were able to rule out hydrogen. I presume that means
they were only *looking* for hydrogen — is that correct? I think of
their work as looking at the spectra from the planet’s atmosphere, so
I can’t understand why they couldn’t say “There’s no hydrogen but
there *is* blah, foo and bar in there.” What have I missed?

And you’re right…this is amazing news. I’m going to have fun
telling this to my kids tonight!

Got me thinking of Tenebra from the novel “Close to Critical” (although there the gravity was very strong, not weak). Note that the atmosphere of this planet is likely to be *really* distended. If it was mostly water vapor at 200 °C, then at around 1 G the scale height is going to be on the order of 10 km. If the ground pressure was high (90 Atm or greater?), then the 1 Atm level (of live steam!) is about 45 km up (!).

A density of 1/3rd the Earth’s is… hard to picture. I’m not sure – would even a pure silicate object, under that self-compression, stay that low? What are the chances that this is perhaps a water-world with almost no metals and perhaps not even dominated by silicates? That would explain low density, as well as an atmosphere consisting of (primarily?) water vapor.

Hmm… if so, the surface of the “ocean” would be set by the pressure and temperature, and those should be workable as an adiabatic profile from the “top” conditions worked on down towards the center… and if you know the actual boundary of that ocean, and the bulk density, then you can make guesses about the portion of silicate vs. water.

Okay, I got really confused reading this article, and thought the planet would be more like a gas giant than a super Earth, with a radius bigger than those of Uranus or Neptune. And the density didn’t match with a mass 2.6 times that of Earth!

So I checked the ESO release, and turns out the data for the mass and radius are the opposite in this post, Phil!

The bigger the planet, the more light is blocked. If the planet blocks, say, 1% of the light, then it has a radius 1/10th that of the star
Don’t you also need to know the distance of the planet from the star? Just a little gedankenexperiment here, but the moon blocks 100% of the sun’s light, and it is not the same radius as the sun.

Phil, I am not so sure about your conclusions.
Carl Sagan would probably say something like that: “Observation: I cant see hydrogen. Conclusion: steam!”. (the original quote was also related to Venus “observation: I cant see a thing. Conclusion: dinosaurs!”).
I think we should try not to get ahead of ourselves. Lets gather more data first!

What I take out of this is how amazing it is that we can detect and discern the properties of an object that’s ~20,000 miles in diameter, from 42 light years away. The actual discovery itself — it’s more of a super-Venus than a super-Earth, isn’t it? — isn’t as fascinating as that.

Phil, I understand that we would weigh basically the same on the “surface” of the planet, but wouldn’t the pressure generated by a 120 mile thick steam atmosphere create pressures that would crush us if we were able to get past the heat and actually “stand” on the surface?

So, can we assume this thing is tidally locked, and start talking about a Weinbaum Venus scenario with giant ice mountains, lit only by a murky twilight and incessant lightning, just beyond the terminator on the Dark Side?

Andrew (14): Deep sea hydrothermal vents on Earth feature superheated (and sometime supercritical) water at temperatures up to 400 C, so a high-pressure, high-temperature water world doesn’t seem all that nonsensical to me. Water has some unusual, nonlinear properties at high pressures.

Deep sea hydrothermal vents are also rich in exotic life (archaea and extremophiles). I imagine there some — how shall I put it? — very interesting chemistry going on in a place like GJ 1214b.

Water vapor is invisible. There is usually water vapor in the air around you, in your room, outside, in your car. You can’t see it. (But it can see you.) And you can see what does. For example, on a high-humidity day, they sky looks kind of whitish. That’s not water you’re seeing; that’s the changing opacity of the air due to the high amount of water vapor in the air. (If it’s foggy, well, that’s a condition where water has condensed (precipitated out of solution, in a chemistry sense), and the drops are so small that it doesn’t take much vertical motion to keep those droplets from falling to the ground.

Steam is (very) tiny drops of water, and usually is mixed with air which has water vapor within it. It is not water vapor (again, which is invisible). Steam is a mixture of water vapor and liquid water due to the properties of water near its local boiling point (which basically depends on altitude). Fog is a similar situation, but steam is where water vapor is changing state into water because the water molecules lose energy from their being away from the source of heat and mixing with less-energetic air.

So, in summary, steam != water vapor, but steam does contain water vapor.

Your article, though is good; this is just something that I felt needed an explanation.

Don’t you also need to know the distance of the planet from the star? Just a little gedankenexperiment here, but the moon blocks 100% of the sun’s light, and it is not the same radius as the sun.

What actually matters is the ratio between the distance from the observer (ie earth) to the planet and the distance from the observer to the star, at the time of transit. It matters for the moon (and I would presume Venus and Mercury as well) because that ratio, obviously, is a number very different from 1.

For extrasolar planets, however, we’re talking about the ratio of x lightyears and x lightyears – (something between a fraction of an AU up to several AU at most), and that is going to be for all intents and purposes within measurement error of 1.0, and washes out of the equation.

Hey, so I have a question – what do we do about stars that are angled relative to us in such a way that their planets will never transit their star? Are we stuck not knowing whether or not they have planets, or are there other ways?

That’s a lot of real estate for a surface gravity similar to Earth. I would love to hear about a planet of similar size and mass in a habitable zone with an oxygen signature. Still, a water vapor dominant atmosphere is very interesting.

Heh.
That CNN report you linked to on twitter, Phil, calling you a wet blanket, well, you know what? I thought exactly the same thing you did, with a rational sensible call on what was going to be announced.

Doesn’t make it any less AWESOME! I mean… WOW water vapour and/or steam (based on the definition of whichever term it is supposed to be)?? An ATMOSPHERE that was MEASURED?? That’s AMAZING, and cool and fascinating and brilliant… and … and… just wow.

Reality is so much cooler and interesting than anything us mere mortals could make up in our little brains!

As far as I can tell from various conference abstracts, it seems more likely this planet is a “mini-Neptune” than a super-Earth. Certainly the modelling that has been done for this object indicates that actual liquid water (even under high pressure) is very unlikely within GJ 1214b: most likely the atmosphere undergoes a smooth transition to a supercritical state.

Chris B. Critter – Coming from an engineer who works extensively with boilers: steam ≈ water vapor. Steam is gasseous water, not an aerosol of liquid water as you describe. You’re talking about fog / mist / clouds. It’s informally called steam when you see it above a pot with boiling water, but the real steam is the invisible part before condensation to mist starts.

The difference between steam and water vapor is that “water vapor” is assumed to be a minority component of a gasseous mixture such as air, while “steam” is assumed to be mostly water vapor with only minimal other components.

I wonder if there is a habitable spot somewhere on the back side… It would obviously not have breathable air, but I wonder if there’s a place where the temperature and pressure would support earth life. It might have to be far up into the atmosphere. The mountain in Niven’s _Gift_From_Earth_ comes to mind.

I wonder if there is a habitable spot somewhere on the back side… It would obviously not have breathable air, but I wonder if there’s a place where the temperature and pressure would support earth life. It might have to be far up into the atmosphere. The mountain in Niven’s Gift From Earth comes to mind.

&

@17. -jeffB :

So, can we assume this thing is tidally locked, and start talking about a Weinbaum Venus scenario with giant ice mountains, lit only by a murky twilight and incessant lightning, just beyond the terminator on the Dark Side?

Nice thought but, alas, I doubt it.

I think (28.) andy’s suggestion of a Hot Mini-Neptune and the isea of a super-heated water planet – a world covered with an immense ocean – is the most likely scenario for what GJ 1214b is like.

My guess as to what’s most plausible is that there’s most likely a thick superheated atmosphere becoming a supercritical (hot fluid /”hot ice”) atmosphere down to a magma rock surface. At no point in this model could human or biological life survive and there really isn’t a particularly solid surface anywhere.

Temperatures and pressures would be excessive even for Venus, chemical composition unknown probably toxic. Also the atmosphere could well be spreading the heat around analogous to Venus meaning there may be no cool or cold zone even if the planet is tidally locked which isn’t certain. (Mercury and Venus after all aren’t tidally locked in our system.)

So imagine you take Venus, drag it right next to the Sun, increase its mass, add a layer of steam and a supercritical superhot fluid ocean and that’s what I think we’ve most likely got in GJ 1214b. Not really a nice place to visit or a plausible habitat for anything remotely like our type of life – although fascinating in its own right.

@24. Eugene Says:

Hey, so I have a question – what do we do about stars that are angled relative to us in such a way that their planets will never transit their star? Are we stuck not knowing whether or not they have planets, or are there other ways?

Good question – yes there are indeed other ways including direct imaging – we’ve actually photographed exoplanets around Fomalhaut and HR 8799 or “Gadolabove”* and 2M1207b plus a few others which are unconfirmed candidiates planets or brown dwarfs. There’s also astrometry – looking for the “wobble” in the stars path produced by the tug of the exoplanets gravity and micro-lensing where a distant star-planet causes a change in brightness of another star. So there’s a range of exoplanet finding techniques with varying strengths and weaknesses.

* The “Gadolabove” name derived from Gamma Doradus Lambda Bootis Vega – noting the other traits of this A5 V Sirian star which is a Gamma Doradus variable, a metal-poor Lambda Bootis star with a Vega – type protoplanetary disk all at once.

To clarify here, 2M1207b is actually the planet itself that was directly imaged NOT the sun it was orbiting. That brown dwarf “star” in question being “named” – if you can call it that – as 2MASS J12073346-3932539 or, as its more often mercifully abbrievated to, 2M1207A.

BTW. Yegods, I wish they’d give these remarkable stars and exoplanets some *proper* pronouncable more easily communicable & more evocative names rather than such awkward, uninspired, hard to memorise catalogue designations! I know there’s too many new-found worlds to give *all* the exoplanets proper names but the more significant ones surely could be given reasonable monikers. I do think doing so would help with better communicating and sharing these exoplanetary discoveries to the wider community.

Now, okay, several of them may end up being classified as brown dwarfs and those in protoplanetary disks suffer from perhaps being technically ineligiable because of the idiocy of the IAU’s anti-Pluto “clearance” balony criterion but still ..

Which was the count as of Nov. 2008.

Since then, hmm.. right now I can’t think of any immediate additions to that list but there might perhaps have been one or two I missed, I guess. Plus we may have clarified the status of some of the boarderline brown dwarf / exoplanet one’s although, again, I’m unaware if this has happened or not. If I remember rightly, there has, sadly, also been some doubt cast over the planetary status of some of these too.

I’m amazed that it can be more massive than Earth and yet having the same surface gravity.

When I watched SW Episode One, I was outraged at that expression “A small planet named Naboo”. I thought that if that planet was really small, then gravity would have to be impossibly weaker. Now I see that the other SW planets may have been bigger, less massive and yet habitable.

I read an article several years ago about DNA remaining stable and functional in liquid water at up to 750 degrees F, if the ends of the DNA helix are joined. In order for the DNA to be functional(biologically active)at what we consider normal temps., the DNA helix has to be open(not joined), as it is for life on earth.

It’s POSSIBLE, if the surface pressure is high enough, for there to be liquid water at that temp and possibly life, if its DNA double helix is joined at the ends.

Only 42 light years? An easy trip, at 10 % light speed, we’d know for sure in only (420 years to travel, plus 42 years for return EM communication)= 462 years to know if anyone is home.

The title of this article makes me want to re-read CS Lewis’ Space trilogy. And I’m actually quite impressed with this. News about exoplanets has been rather bland the last few years so it’s nice to have more detailed discoveries to spice it up a bit!

I’m amazed that it can be more massive than Earth and yet having the same surface gravity. When I watched SW Episode One, I was outraged at that expression “A small planet named Naboo”. I thought that if that planet was really small, then gravity would have to be impossibly weaker. Now I see that the other SW planets may have been bigger, less massive and yet habitable. …

Well “small” is a relative term.

Earth is very small relative to Jupiter but very large compared to Pluto.
Pluto in turn is small relative to Earth but is large relative to Sedna, Ceres and Vesta.

So it all depends.

If we’re talking habitable planets then Mars is just a bit too small – too lacking in mass to hold onto its atmosphere, keep its intenal dynamo going to create a planetary magnetic field and to have plate tectonics and lithographic (geological) cycle.

Naboo you might think is just big – in radius and more importantly massive -enough too all those things.

In the text ‘Planets for Man’ by Stephen Dole & Isaac Asimov (New York, Random House, 1964.) based on a Rand study and dedictaed to assessing the nature and probabilities of habitable planets it was suggested that the range of masses for a habitable planet extends from 2.35 times the earth’s mass at the large end down to 0.40 at the small end. In other words the least massive habitable planet they suggest will be just under half Earth’s mass.

Perhaps that’s about where Naboo is.

Mars Btw. has a mass of 0.1077* and yet was possibly habitable early on in its astronomical history and may one day be again if we ever successfully terraform it.

Or, as 39. QuietDesperation suggests, it could be that the use of ‘small’ there is referring to Naboo’s population, political significance and economic size.

If I understand correctly, it’s entirely possible for a planet with a smaller radius then the earth to have the same surface gravity, assuming that planet is denser then the Earth.
However, the earth does have an iron core, so it’s toward the dense end of the scale already. Also, didn’t Naboo have that ridiculously deep ocean that allowed them to travel a portion of the way around the planet by taking a shortcut through some deep subsea passages? A planet that porous with that much water isn’t going to be all that dense…

Naboo is described as having a porous, plasma-rich interior without a molten core—a rare phenomenon among the planets in the Star Wars universe. The surface of Naboo is covered by dense swamps, rolling grass plains, and verdant hills. … Underneath the planet’s surface is a tremendous maze of passages and caves, home to immense aquatic animals and creatures that are never seen on the surface. Gungans dominate these ‘underwaterways’, using them as a highway of sorts between their surface Holy Places and their underwater cities. One gungan civilization was known as Otoh Gunga, where Jar-Jar leads Obi-Wan Kenobi and Qui-Gon Jinn.

As for :

“If I understand correctly, it’s entirely possible for a planet with a smaller radius then the earth to have the same surface gravity, assuming that planet is denser then the Earth.

Agreed – and also vice versa a larger more porous planet may well have the same surface gravity of Earth even though its radius is larger.

I did see an article somewhere earlier this year on planet types with a good chart /diagram of this concept with worlds ranging from low density high radius Ocean world types to high density Iron Cannon Ball ones – but, unfortunately, I forget which magazine that was & can’t find it right now.

the water vapor planet could be us 10 mya, red, humid, unlivable except at the mountain tops with springs and the last water pools down below. Where is the water, up in the atmos held there by electricity; the charge weakens and down the water falls.
arsenic, our poison, now acceptable in pork, chickens and i suspect cattle. The hog farm people tout the arsenic occurring naturally in the water arising eons ago when the Carolina meteorites impacted the coastal areas, as being good for the pork, meaning you naturally, as it kills the trichinosis worm suddenly found less in pork.